The existence of a new unique form of carbon, the fullerene, was first demonstrated by Kroto et al. in 1985 [1]. Tubular structures of carbon, closely related to the fullerene (called carbon nanotubes) were first synthesized in an arc discharge by S. Iijima[2]. Carbon nanotubes can be synthesized in two forms, multi-walled and single-walled tubes. Particularly, single-walled carbon nanotubes have many unique and potentially useful physical and chemical properties [3].
Several methods for the production of carbon nanotubes and fullerenes have been successfully demonstrated in the past decade. The principle methods used to obtain desired carbon structures include arc discharges [4,5], laser ablation of graphite targets [6], and chemical vapor deposition [7]. These techniques are capable of producing milligram to gram quantities of particularly single-walled carbon nanotubes in a few hours. However, many potential applications of these nanotubes require much larger quantities. So far no process has been described that can produce industrial scale quantities of nanotubes.
A particular disadvantage of the aforementioned techniques lies in the fact that they cannot be continuously operated. Smalley et al. [8] recently developed a continuous flow-through process which is possibly capable of scale-up to large quantities. Carbon monoxide is heated in an oven to temperatures of around 1000° C. to drive the CO disproportionation to form carbon atoms. The formation of carbon clusters, in particular single-walled carbon nanotubes, is enhanced by adding gaseous iron pentacarbonyl to the gas mixture in the oven.
Since their discovery in the mid-80's, much effort has been put into the study of fullerenes. Although many potential applications have been proposed, these fullerenes have not lived up to their potential. Interest has since shifted to carbon nanotubes, particularly single-walled carbon nanotubes.
Initial tests suggest that carbon nanotubes may be promising materials for hydrogen storage, a property of great interest to the automobile industry in the search for cleaner running automobiles. The use of fuel cells in automobiles is presently inhibited by the lack of an effective hydrogen storage medium. The use of carbon nanotubes in this field is therefore being extensively explored.
Another potential application involves use of carbon nanotubes as electron emitters in field emission displays. Liquid crystal displays currently dominate the market for flat panel displays. Their major disadvantage, however, lies in the expense of production and the comparatively poor quality of display. Field emission displays are expected to be far superior, with nanotubes providing cheaper electron emitter production.
Finally, nanotubes demonstrate an opportunity for the synthesis of carbon containing materials with very promising characteristics such as extreme hardness, low density, and variable conductivity. There are also interesting applications for such light materials in the aerospace, automobile or sports article industries.
A present disadvantage for the industrial use of carbon nanotubes in the applications presented above is the fact that, to date, a system for synthesizing large quantities of nanotubes has not been found. Most techniques operate on a gram per day basis and require subsequent cleaning of the material, leading to prices of about $2000 per gram for 85% pure material.
It is therefore an object of the present invention to develop a system and method for cheaply and efficiently producing industrial quantities of single-walled carbon nanotubes.
Although described with respect to the field of carbon synthesis, it will be appreciated that similar advantages may obtain in other applications of the present invention. Such advantages may become apparent to one of ordinary skill in the art in light of the present disclosure or through practice of the invention.